Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Life habit: lichenicolous, parasitic, non-lichenized Ascomata: peritecioid pseudothecia, subglobose, ovoid or ob-pyriform, dark brown or black, ostiolate, immersed, semi-immersed or subsessile, scattered or in smalls groups, sometimes confluent in necrotic patches or in gall-like deformations of the host thallus ascomatal wall: entirely brown to dark brown, frequently with green tonality near the ostiolar zone, pseudoparenchymatous, composed of several layers of isodiametric to tangentially elongated cells, with brown pigmented cell wall hamathecium: in the mature perithecia formed by paraphysoids and periphyses, hyaline, I-, K/I-; paraphysoids: well developed, numerous, remaining distinct, filiformes, hyaline, septate, abundantly branched and anastomosed; periphyses: ostiolar filaments clearly differentiated, branched, hyaline, in some species green pigmented at the top of the ostiolar region asci: clavate to subcylindrical, distinctly stipitate, bitunicate (fissitunicate), thickened with a distinct internal apical beak at the apex, I-, (2-)4- or 8-spored ascospores: brown or dark brown in the oldest, with the tips of the end cells often pale brown to subhyaline, ellipsoid to broadly fusiform, often slightly curved, rounded or obtuse at the apices, usually 3-septate, rarely 2- or 4-septate; in some species several additional, characteristic, small, 1-septate spores are always present in the asci; usually with a conspicuous pore at the central part of the septa, constricted at the septa or not; smooth-walled Conidiomata: pycnidial, black, immersed, with a dark brown wall conidia: hyaline, simple, short-oblong Geography: cosmopolitan Substrate: thallus of lichens occurring on bark, rocks, soil, bryophytes or living leaves. Notes: In the description of the genus Pyrenidium the characteristics of P. hyalosporum are excluded, a species that grows on Placopsis gelida and that, in our opinion, does not belong to this genus according to the description provided by Alstrup and Hawksworth (1990). This species differs from the other of species of Pyrenidium in having colorless ascospores provided in the subapical part of a structure that resembles a geminative pore, and in lacking a central pore in the spores septa. Other differences observed in the studied specimens of P. hyalosporun are the absence of periphyses in the hamathecium, and the predominance of 1-2-septate ascospores, only exceptionally 3-septate, with length over 30 µm, which exceeds the spore size of any other species included in Pyrenidium.